In order to haul the heavy payloads generated from mining rock and minerals from the earth, such as those excavated from an open-pit mine or quarry, a large off-highway, heavy-duty work vehicle 100, such as that shown in FIG. 1, is typically required. This type of heavy-duty vehicle 100 employs motorized wheels for propelling and retarding the vehicle 100 in an energy efficient manner, where the energy efficiency is typically achieved by employing a large horsepower diesel engine 102 in conjunction with an alternator 104 and a main traction inverter 106. The diesel engine 102 drives the alternator 104 in order to power the main traction inverter 106, which controls the voltage and frequency of the electric power being supplied to drive motors 108 disposed within the rear wheels 110 of vehicle 100. As drive motors 108 are operated, the drive motors 108 cause a transmission drive shaft to rotate at a low torque and high speed about the drive shaft axis. The transmission drive shaft transfers this low torque high speed rotational energy to the vehicle transmission which converts this energy into a high torque low speed rotational energy output that is supplied to the rear wheels 110.
Referring to FIG. 2, the alternator 104 used in this type of vehicle is typically a main 3-phase traction alternator having a rotor 112 that is directly associated with the output shaft of the diesel engine 102 such that any rotational movement of the output shaft translates into rotational movement of the rotor 112. Thus, when the diesel engine 102 is operated, the rotation of the output shaft causes a corresponding rotation of the alternator rotor 112. When an excitation current is applied to the field windings of the rotating rotor 112, a voltage is generated in the armature windings on the stator of the alternator 104 responsive to the rotation of the rotor 112. Thus, it follows that the output power of the alternator 104 is responsive, at least in part, to the rotational speed of the engine 102. As such, the faster the output shaft rotates, the faster the alternator rotor 112 rotates and the more power is generated by the alternator 104.
In order for heavy-duty work vehicles 100 to be able to haul their heavy payloads or to accelerate from rest, a large amount of power is needed. Because the power generated by the alternator 104 is proportional to the rotation of the alternator rotor 112, as discussed hereinabove, the alternator rotor 112 must be rotated at speeds up to 1900 revolutions per minute (RPM's) in order to generate the amount of power required to propel these vehicles 100. It is well known that rotor rotational speeds this high generate a large amount of stress loads (both centrifugal and axial) on components disposed within the alternator 104, such as a plurality of connection straps 116 which are used to connect the alternator winding sets together in a series fashion.
As shown in FIG. 2, FIG. 3 and FIG. 4, current tie ring assembly designs employ a fiberglass tie ring body 118 which provides support to the plurality of connection straps 116. These connection straps 116 typically include a first strap connector 120 associated with a second strap connector 122 via a strap body 124, wherein the strap body 124 is associated with the tie ring body 118 using clamps and/or tape. The connection straps 116 are used to connect like poles from each set of alternator windings in a series fashion, wherein first strap connector 120 is connected to a pole from one set of alternator windings and second strap connector 122 is connected to the like pole from an adjacent set of alternator windings. Because each set of alternator windings has at least two poles, two connection straps 116 are typically required to connect one set of alternator windings to an adjacent set of alternator windings. Moreover, because one pole is disposed on one side of the set of alternator windings and the other pole is disposed on the opposing side of the set of alternator windings, there may be connection straps 116 disposed on both the internal and external surfaces of the tie ring body 118. Unfortunately however, as the alternator rotor 112 is rotated at high speeds, large centrifugal forces Cf are generated, as shown in FIG. 5. This centrifugal force Cf produces a tendency in the connection straps 116 to move away from the axis of rotation h, disposed in the center of the alternator rotor 112, in a direction perpendicular to the external surface of the tie ring body 118.
This can be seen more clearly by referring to FIG. 5, where a top down view of alternator rotor 112 is shown having only tie ring body 118 and a plurality of connection straps 116. Plurality of connection straps 116 include a plurality of internally disposed connection straps 126 and a plurality of externally disposed connection straps 128, wherein internally disposed connection straps 126 and externally disposed connection straps 128 connect one pole of one set of alternator windings to a similar pole of an adjacent set of alternator windings. As the alternator rotor 112 is rotated about its axis h, in this case in the clockwise direction, a centrifugal force Cf (represented by the arrows in FIG. 4) is generated producing a tendency in the strap body 124 of both the internally disposed connection straps 126 and the externally disposed connection straps 128 to move away from the axis of rotation h in a direction perpendicular to the external surface of tie ring body 118.
As the centrifugal forces Cf increase, the tendency of the internally disposed connection straps 126 to move away from the axis of rotation is counteracted by the internal surface wall of tie ring body 118. Thus, the stresses on the internally disposed connection straps 126 due to centrifugal forces Cf are essentially equalized by the internal surface wall of the tie ring body 118. However, as the centrifugal forces Cf increase, the tendency of the externally disposed connection straps 128 to move away from the axis of rotation is counteracted only by the clamps and tape holding the externally disposed connection straps 128 to the external surface of tie ring body 118. As the clamps and tape wear with use and age, the strap body 124 begins to move becoming less secure. This puts stress on the connection between the first strap connector 120, the second strap connector 122 and the poles of the windings.
Although this design provides sufficient support for tie rings on vehicles that generate alternator rotor rotation speeds of approximately 1050 RPM's, such as a locomotive, this design is inadequate to provide the support needed to sustain the higher stress loads generated by the higher rotor rotation speeds of large off-highway heavy duty work vehicles 100, due to centrifugal forces, axial forces, thermal expansion and vibrational forces. Because of this design limitation, the larger rotation speed decreases the life span of the connection strap 116 and increases the probability that connection strap 116 may fail, possibly causing extensive and/or irreparable damage to the alternator. Thus, at the very least, a failure of connection strap 116 may require that the alternator be removed and connection strap 116 be replaced and at the very worse, a failure in the connection strap 116 may irreparably damage the alternator. Each of these scenarios is undesirable because alternators of this type are very large, very heavy, very cumbersome to work with and very expensive to replace and repair.